Performance regression due to font rendering

[dlh]

Font rendering in 0.4 and trunk has introduced a huge performance regression compared to 0.2.8.

Our usage of FTGL could be improved:

• Restrict our font size usage to 1 or 2 sizes and scale before rendering. This will generate only 1 or 2 OpenGL textures compared to now where a new texture is generated for every font size.
• Minimize or cache GetWidth() calls that determine the width of a to-be-rendered string.

FTGL development seems to be dead but it could also use some optimizations, such as better glyph packing in the texture object. Currently FTGL creates a large texture object where glyphs are packed into a single row (ex: 8162px by 16px with a full-featured TrueType font).

We could also move to something like freetype-gl <https://github.com/rougier/freetype-gl>, but that presents new problems—it exclusively uses wchar_t.